Plastic containers are widely used in many applications requiring thermal stability up to about 185° F. while maintaining the physical integrity of the container. In some applications, however, the package must be processed at even higher temperatures. Low-acid packaging applications frequently require, for example, processing temperatures above 200° F. Still other applications require processing temperatures at or above the boiling point of water (about 212° F.). Such elevated-temperature processing may contribute to intensive evaporation of the liquid stored in the container, expansion of the contained gases that develop at the elevated pressures, or both. The pressures that develop can vary from positive pressure (above atmospheric) upon heating to vacuum during and after cooling, conveying, and storing processes. Cooling processes can be performed at or near the freezing point of water (32° F.) and even at subzero temperatures.
Conventional plastic containers exposed to such conditions can distort by bulging and can implode during cooling. The distorted container often loses its ability to seal and maintain air and liquid-tight closure due to distortion of the container finish. The distorted container also loses its shape noticeably enough that labeling and printing on the surface of the container are rendered difficult, if not impossible. In addition to these functional drawbacks, the distorted container loses its aesthetic consumer appeal.
To overcome the problems identified above, many conventional containers have panels, indented handles, ripples, and stiffeners of various forms. These components increase the weight and the cost of the container, and substantially reduce the area on the container available for labels and print. It is also a common practice to increase the wall thickness in order to stiffen the container. This practice often leads, during packaging operations, to partial or full heat-induced crystallization of the polymer used to make the container. Such crystallization leaves the container pearlescent or opaque, irreversibly and adversely affects the structural integrity of the container, and detracts from the consumer appeal of the container. Several patents and published patent applications have also tried to address the problems identified above. Samples of those patents and applications are summarized below.
In U.S. Patent Application Publication No. 2008/0083693, Gottlieb et al. describe a flexible membrane that is movable in response to a change in pressure inside a bottle, allowing for pressure equalization as the bottle cools. The cap for the bottle has an outer cap and an inner cap, with the flexible membrane positioned in and attached to the inside of the inner cap. An air-tight seal is formed between the flexible membrane and the bottle rim when the cap is attached to the bottle. The inner cap has an aperture allowing air to enter the area between the flexible membrane and the cap. The flexible membrane remains attached to the cap when the cap is on the container or is removed. Although the disclosed device compensates for the vacuum developed in the container during cooling, its complexity is economically prohibitive and it provides an entrance path for bacteria into the space under the cap.
In U.S. Patent Application Publication No. 2007/0131644, Melrose describes a container, intended for filling with a hot liquid, and a headspace sealing and displacement method for removing vacuum pressure. The container has a neck finish with an opening closed by a primary seal which has an expandable side wall. As the liquid cools, the side wall is drawn into the container to remove vacuum pressure created within the container. A permanent cap can provide a secondary seal for the container and define a secondary headspace between the primary and secondary seals. In other embodiments, the primary seal can be replaced by a mechanically movable seal which may be locked in its downward position. The secondary seal can also have a port or an aperture to provide access into the secondary headspace for a commodity such as a tablet or pill. The container disclosed by Melrose has multiple components, and the disclosed method requires two or three independent operations. Moreover, the container and method do not sufficiently compensate for the positive pressure created during filling and closing operations.
Marbler et al. teach closure membranes for containers in U.S. Pat. No. 6,182,850. The membranes include a number of functional layers, some punctured to allow the pressure in the interior of the container to be adjusted to the atmosphere. A chemical organic material, such as hot melt, paraffin, wax, or the like, softens under the influence of heat and closes the punctured layers during hot fill or pasteurization operations. Alternatively, in another stage of the manufacturing operation, the membrane can be completely sealed. Although the closure membranes compensate for the positive pressure during the filling operation, they provide an entrance for bacteria to enter the under-cap space and fail to compensate for either positive or negative pressure after sealing and during the life of the product.
Bartur et al. disclose a pressure-equalizing and foam-eliminating cap for a container in U.S. Pat. No. 5,853,096. The cap is specifically designed to accommodate liquids and vapors at higher-than-atmospheric pressure. The disclosed cap relates to bottle caps which allow for pressure equalization at opening and which eliminate the release of a mixture of gas and liquid from the interior of the container upon opening. The cap works well for pressures above atmospheric, such as in packaging of carbonated beverages and where user intervention is present to safely open the container. The rigidity of the construction renders the cap less well suited, however, to compensate for the vacuum pressure generated during processing of hot-fill and pasteurizable containers.
In U.S. Pat. No. 4,174,784, Hartung discloses an anti-collapse cap. The device prevents the inward deformation of a hollow plastic container which would normally inwardly deform after closure due to the cooling of hot liquids in the container. The device has a membrane with peaks and valleys extending across the container spout to seal the spout. The membrane is formed of a single unitary piece of flexible material that is more flexible than the walls of the container. The ambient pressure on the outside of the container is applied to the outside of the surface of the membrane. The device disclosed by Hartung is expandable and inwardly deforms when, after sealing, there is a pressure reduction within the container. Although the disclosed cap compensates for the vacuum which occurs in the container after cooling, the cap would be inefficient under the high temperature and pressure in hot fill and pasteurizing applications where excessive internal pressure develops due to the evaporation of fluids in the container.
In their International Publication No. WO 2006/053013, Trude at el. describe a moveable seal for a hot-fill or pasteurizable container. The seal moves in response to pressure changes in the container and has a number of collapsible vertical bellows that can be folded next to one another to extend into the container or toward the closure depending on the pressure inside the container. The moveable portion of the seal can take the shape of ribs or concentric circles that are placed throughout the entire device. The Trude et al. seal is a pressure-compensating device that can respond to either positive or negative pressure, but requires an expensive multi-step folding operation during manufacture. For high-temperature applications, the seal requires an additional dip-annealing operation to assure a spring-like response. Such an operation would make the device economically infeasible. Further, the bellows construction has a vertical configuration that limits the range of motion for the seal. Still further, although it is particularly suitable for long-to-medium neck containers, the seal has structural limitations in short neck and extra wide-mouth container applications. Finally, the disclosed seal consumes container volume that might otherwise be designated for the product retained inside the container.
Many, if not all, of the devices described in the patents and applications summarized above have a variation of a vent hole which presents the risk of tampering with the product. Many of the devices are too complex to economically manufacture. Others are designed to equalize excessive pressure or vacuum but not both. Some devices consume a substantial amount of container volume. Others are vertically activated, presenting an opportunity for the device to collapse under vacuum or high-pressure pasteurization.
Therefore, there remains a need in the art for an improved container closure diaphragm that responds to the differential pressure inside of the container by translating forces into motion via deflection. The present invention provides an apparatus that meets this need and overcomes the shortcomings of the current solutions. The present invention also provides an apparatus that meets the related need for an economical and efficient way to adapt presently available standard containers with a variety of necks and finishes and standard caps as a part of a packaging solution. It is a principal object of the present invention to provide an apparatus that can be hot filled or pasteurized. A related object is to provide an apparatus that compensates equally for both the high pressure and vacuum conditions that occur during hot-fill and pasteurizing processes. Another object is to protect containers and caps from varying pressures at elevated temperatures and after cooling. Still another object is to provide an apparatus that does not consume a substantial amount of container volume designated for the product.